The present invention relates to technologies pertaining to liquid crystal panel driving devices used for driving liquid crystal display devices that employ a so-called active matrix liquid crystal panel in which an electric charge is stored in between an opposing electrode and pixel electrodes by applying voltages corresponding to image data to the pixel electrodes through source lines and pixel switches.
An active matrix type liquid crystal display device has, as shown in FIG. 21, for example, a liquid crystal panel 907, a gate driver 908, and a source driver 909. The liquid crystal panel 907 comprises a liquid crystal layer 901, pixel electrodes 902, opposing electrodes 903, pixel switches 904 comprising TFTs (Thin Film Transistors), gate lines 905, and source lines 906.
The gate driver 908 sequentially applies drive pulses to the gate lines 905. The source driver 909 applies voltages corresponding to image data for the respective pixels to the source lines 906. Specifically, the source lines 906 receives the voltages that successively change corresponding to image data for the pixels corresponding to the gate lines 905 to which the sequential drive pulses are input, and the voltages are retained in between the pixel electrodes 902 and the opposing electrodes 903 (in a liquid crystal capacitance), so that images are displayed.
In such liquid crystal display devices as described above, power is consumed mainly because of the electric current flow that charges and discharges the liquid crystal capacitance and the parasitic capacitance in the source lines 906 at the time when the applied voltages to the source lines 906 change. Especially when a line inversion drive, in which the polarities are reversed in every other set of pixels corresponding to the gate lines 905 adjacent to each other, is carried out to prevent picture quality degradation, the charge-discharge current that flows each time of the polarity reversal is large, and therefore, power consumption tends to be large even when the difference in display contrast among pixels is small.
Reducing the power consumption as described above is an important issue for, for example, devices that need to be driven by batteries for long hours, as exemplified by portable terminal devices such as mobile telephones, which have rapidly become widespread. In view of this, various technologies have been proposed to reduce the power consumption as described above.
For example, Japanese Unexamined Patent Publication No. 2000-221932 discloses the technology as follows; before the source driver newly applies voltages to source lines, all the source lines are temporality connected to each other to average the potentials of the source lines, and thus the current flow is reduced at the time when the source driver applies voltages corresponding to image data.
Also, Published Japanese Translation of PCT publication No. 9-504389 discloses a technology in which, before the source driver newly applies voltages to source lines, a capacitor is connected to the source lines so that an electric charge is stored into the capacitor or the stored charge is discharged therefrom, in order to average the potentials of the source lines.
Japanese Unexamined Patent Publication No. 10-222130 discloses the following technique. Using a capacitor for positive polarity and a capacitor for negative polarity, for example, before applying a negative voltage after a positive voltage has been applied, the capacitor for positive polarity is first connected to the source line to store a positive electric charge in the capacitor and to reduce the potential of the source line, and next, the capacitor for negative polarity in which a negative electric charge is stored is connected to the source line to further reduce the potential of the source line. This technique is intended to reduce the current flow at the time of the subsequent negative voltage application.
These conventional liquid crystal panel driving devices, however, have a problem in that none of them can reduce the power consumption significantly. Specifically, when all the source lines are connected to each other uniformly or capacitors are connected thereto, every source line is made to have an average potential, For this reason, when a voltage is applied at a similar magnitude to that applied previously, it is necessary to supply an electric charge to raise or reduce the potentials of the source lines once again. This causes an unnecessary electric charge shift, which correspondingly increases power consumption. Moreover, when capacitors are connected twice each time a voltage corresponding to image data is applied to the source lines, as described in Japanese Unexamined Patent Publication No. 10-222130, the time required for the sequence becomes long. This may cause a problem in that it is difficult to display images at an appropriate scanning frequency.